This invention is for the radiation treatment of targets that move due to a physiological process. Especially the treatment of pulmonary nodules that move due to respiration. The treatment margin that is required because of uncertainty of nodule location can be reduced to about 3 mm if treatment planning image capture and radiation treatment both occur when the patient is in a relaxed exhalation respiratory state. An object of the present invention is to further reduce the margin to about 1 mm by using a radiographic imaging system to capture images of the nodule immediately before and/or during radiotherapy.
For this purpose, the present invention provides improvements to an existing image segmentation method so that this method can be used for the special case of localizing a nodule in a radiograph. Based on the location of the nodule in the radiograph treatment may be modified by withholding irradiation, moving the patient, or moving the therapeutic beam to better target the nodule.
The present invention is described in the context of localizing a nodule in a single radiographic image. However, it should be understood that this invention includes localizing a nodule in more than one radiograph at approximately the same time in order to determine the location of the nodule in three-dimensional space. In this invention, a nodule is a mass of any shape and size. The nodule may benign or malignant.
Automatic determination of the location of an nodule in a radiograph can enable radiography to be used for near real-time nodule localization during medical procedures. Unfortunately, the localization of a nodule in a radiograph is generally very difficult because a radiographic image is a superposition of the radiodensity of all tissue in the path of the X-ray beam. Overlapping and surrounding structures often confound segmentation methods that determine the region in the radiograph that is occupied by the nodule.
The ability of a segmentation method to localize a nodule is greatly enhanced by the use of information that is obtained from the planning image on the characteristics of the nodule as disclosed in commonly-assigned U.S. patent application Ser. Nos. 11/039,422 and 11/221,133. However, the planning image is often a tomographic image that is captured at a lower resolution than is typical of a radiographic image. It is a goal of this invention to provide an image processing means to localize a nodule in a radiograph with a higher degree of accuracy than is possible by existing image segmentation methods including those that use prior information.